1. Field of the Invention
The invention relates to a hook structure for a spiral spring. More specifically, the invention relates to a hook structure for spiral springs in which a small spiral spring is arranged inside a large spiral spring and in which an inner end of the large spiral spring and an outer end of the small spiral spring are both hooked in a latch provided between the springs.
2. Description of the Related Art
Conventionally, a structure with an urging spring, which constantly applies a forward urging force to a seatback, is used to assist in adjusting the reclining angle of the seatback. Japanese Patent Application Publication No. 2008-54712 (JP-A-2008-54712), describes a structure in which a first spiral spring, which constitutes the above urging spring for the seatback, and a second spiral spring, which is smaller than the first spiral spring, are arranged side by side in a side coupler on one side of a vehicle seat as a coupler between the seatback and a seat cushion.
The inner end of the first spiral spring is hooked to a latch that is cut and raised from the frame of the seat cushion and the outer end is hooked to a bracket that is integrally formed with the frame of the seatback. The second spiral spring serves as an auxiliary member that returns an operation lever to its original position after the operation lever is used to release a locked state of a reclining device that locks a reclining angle of the seatback.
The second spiral spring is formed small enough to fit within an inner space of the first spiral spring and housed in the inner space. More specifically, the inner end of the second spiral spring is hooked to one end of an operation shaft that unlocks the reclining device connected with the operation lever. The outer end of the second spiral spring is hooked to the latch to which the inner end portion of the first spiral spring is hooked.
As described above, because the inner end portion of the first spiral spring and the outer end portion of the second spiral spring are both hooked in the latch formed in the frame of the seat cushion, both of the spiral springs are arranged in a small size, and thus the rational structure can be obtained.
Conventionally, the latch is formed in the frame of the seat cushion to hook the inner end of the large spiral spring and the outer end of the small spiral spring, and is formed as a curved plate that curves along the inner peripheral surface of the first spiral spring. Accordingly, the end portions of the spiral springs that are folded and hooked interfere with each other, and thus it is difficult to hook these end portions together in the single latch.